Coenzyme Q is an essential component widely distributed in living organisms from bacterium to a mammal, and is known as a constituent component of an electron transport system of mitochondria in the cells of living organisms. It is known that coenzyme Q performs a function of a messenger component in an electron transport system by repeating oxidation and reduction in mitochondria, and that reduced coenzyme Q has an antioxidant action. In human, coenzyme Q10, which is coenzyme Q having a side chain with 10 repeated structures, is the main component, and about 40-90% is generally present as reduced type in the living body. The physiological action of coenzyme Q includes activation of energy production by mitochondria activating action, activation of cardiac function, cellular membrane stabilizing effect, cell protection effect by antioxidant action and the like.
Coenzyme Q10 currently produced and sold is mostly oxidized. In recent years, reduced coenzyme Q10 that shows high oral absorbability as compared to oxidized coenzyme Q10 has also been released in the market and is increasingly used.
A general method for obtaining reduced coenzyme Q10 has already been disclosed (patent document 1). As for a method for obtaining reduced coenzyme Q10 as crystals, some methods are known. For example, a method including crystallizing reduced coenzyme Q10 in an alcohol solution and/or a ketone solution to produce crystals (patent document 2), a method including crystallizing reduced coenzyme Q10 in a solvent containing citric acids and/or ascorbic acid (patent document 3), a method including crystallizing reduced coenzyme Q10 by adding a high concentration liquid phase thereof into a poor solvent (patent document 4) and the like have been reported.
In addition, it has been disclosed that a crystal superior in stability and having an X-ray diffraction pattern different from that of general reduced coenzyme Q10 crystal can be obtained by dissolving reduced coenzyme Q10 in fats and oils and cooling same (patent document 5).
It has been reported that, generally, whether organic compound or inorganic compound, many compounds have plural crystal forms having different crystal structures, and this is called crystal polymorph. Such plural crystal forms present in crystal polymorph show not only different patterns in analyses such as X-ray diffraction, infrared spectroscopic analysis and the like, but also different properties such as melting point, solubility and the like. When the substance has a physiological activity of pharmaceutical products, functional foods and the like, the substance sometimes shows different bioavailability. It is commonly known that crystal polymorph should be strictly controlled by, for example, setting the judgment criteria for the content of each crystal form in a pharmaceutical product, and the like, when such difference in the crystallinity affects the function of a preparation, bioavailability or stability (non-patent document 1).
On the other hand, it is also true that the crystal polymorphism has not been elucidated sufficiently. While serious phenomena have been reported wherein the dosage form of a pharmaceutical product already placed in the market needs to be changed, or the development strategy of a pharmaceutical product under development needs to be changed or cancelled, because a new crystal form suddenly emerges one day and a crystal form present until then is no longer obtainable, what causes such phenomena has not been clarified to date (non-patent documents 2, 3).